This folk trio today is remembered as a joke and for the often misinterpreted song "Puff the Magic Dragon." (It's about an effing dragon, if you're curious.) That's a shame: Peter, Paul & Mary were an integral part of the '60s folk movement that eventually brought together the disparate American sounds that gave birth to rock.
Songs like "If I Had a Hammer," a Pete Seeger smash, were legitimate in a time when folk songs were more than entries in a personal diary. PP&M saw the acoustic guitar and the folk festival as agents of social change, and they were successful inspiring exactly that.